The present invention relates to container covers and in particular to flexible covers with improved means for securing the cover to a container.
In the packaging of consumable articles and particularly items such as cakes, biscuits or the like, it is desirable that they be packaged in a manner to assure the freshness of the item. Thus it is desired that they be reasonably well sealed and not inadvertently removed. With articles such as cakes, breakfast rolls or the like which may include frosting or other coatings for taste as well as ornamentation, it is desired that the packaging does not contact the frosting or coating which would cause its mutilation when opening the packaging. Further, it is desired to package such items in a transparent display to visibly promote the product therein.
In order to meet these requirements, in the past cake tins typically made of an aluminum foil tray having a rolled edge for strength have been covered with a flexible, transparent plastic cover made of, for example, polystyrene which extends over the edge of the tray holding the cover on the tray and yet permitting relatively easy removal of the cover. The problem, particularly with relatively large-size, rectangular trays, is that the relatively lengthy sidewalls of the container cover easily bulge outwardly and form an imperfect seal between the cover and the associated tray. This failure of prior at devices to securely seal the container causes rapid drying of the product thereby losing its freshness and saleability.
The prior art includes various closure devices typically having multiple engaging surfaces for assuring a tight seal between a container and its cover. Such prior art is perhaps best represented by U.S. Pat. No. 3,055,540 issued Sept. 25, 1962, to A. Ringlen. In this patent, the container and its cover include several mating, angled surfaces. The container is specially curved to provide a compressive fitting between the cover and the container. Although such prior art devices provide the desired sealing important in the environment of the present application, to achieve this sealing effect the lid and the container itself must be specially manufactured so that they have correspondingly mating, sealing surfaces. It is desirable, therefore, to provide a container cover which will fit with a standard aluminum foil tray or container without modification and yet prevent inadvertent removal and provide the desired sealing not obtainable by known prior art covers for such trays. Since these trays tend to differ in manufactured size tolerances, it is desired also to provide a cover which will accommodate such variations and provide a locking fit for the cover on a given size tray.